The present invention relates generally to the field of polishing pads for chemical mechanical polishing. In particular, the present invention relates to conditioned polishing pads useful for chemical mechanical polishing magnetic, optical and semiconductor substrates.
In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited onto and removed from a surface of a semiconductor wafer. Thin layers of conducting, semiconducting and dielectric materials may be deposited using a number of deposition techniques. Common deposition techniques in modern wafer processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) and electrochemical plating, among others. Common removal techniques include wet and dry isotropic and anisotropic etching, among others.
As layers of materials are sequentially deposited and removed, the uppermost surface of the wafer becomes non-planar. Because subsequent semiconductor processing (e.g., metallization) requires the wafer to have a flat surface, the wafer needs to be planarized. Planarization is useful for removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches and contaminated layers or materials. Planarization is measured at the wafer scale in terms of uniformity. Typically, thin film thickness is measured at tens to hundreds of points on the surface of the wafer, and the standard deviation is calculated. Planarization is also measured at the device feature scale. This nanotopography is measured in terms of dishing and erosion, among others. Typically nanotopography is resolved at higher frequency, but measured over a smaller area.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize or polish workpieces such as semiconductor wafers. In conventional CMP, a wafer carrier, or polishing head, is mounted on a carrier assembly. The polishing head holds the wafer and positions the wafer in contact with a polishing layer of a polishing pad within a CMP apparatus. The carrier assembly provides a controllable pressure between the wafer and polishing pad. Simultaneously, a slurry, or other polishing medium flows onto the polishing pad and into the gap between the wafer and polishing layer. To effect polishing, the polishing pad and wafer typically rotate relative to one another. The wafer surface is polished and made planar by chemical and mechanical action of the polishing layer and polishing medium on the surface. As the polishing pad rotates beneath the wafer, the wafer sweeps out a typically annular polishing track, or polishing region, wherein the wafer's surface directly confronts the polishing layer.
Important considerations in designing a polishing layer include the distribution of polishing medium across the face of the polishing layer, the flow of fresh polishing medium into the polishing track, the flow of used polishing medium from the polishing track and the amount of polishing medium that flows through the polishing zone essentially unutilized, among others. One way to address these considerations is to provide the polishing layer with a grooved macro-texture. Over the years, quite a few different groove patterns and configurations have been implemented. Typical groove patterns include radial, concentric-circular, Cartesian-grid and spiral, among others.
In addition to distribution and flow of polishing medium, groove pattern and configuration affect other important aspects of the CMP process, and ultimately wafer planarity, such as polishing rate, edge effect, dishing and others. Furthermore, groove pattern and configuration affect wafer planarity through a phenomenon known as “groove pattern transfer.” The result of this phenomenon is that certain groove patterns result in the creation of coherent structures on the surface of the wafer corresponding to the pattern of the grooves on the polishing pad. Importantly, circumferential grooves (grooves which make small angles with a line tangent to polishing pad velocity), i.e. circular grooves, circular x-y grooves or spiral grooves, produce a more pronounced groove pattern transfer effect than x-y grooves or radial grooves.
Polishing pad conditioning is critical to maintaining a consistent polishing surface for consistent polishing performance. Over time the polishing surface of the polishing pad wears down, smoothing over the micro-texture (“glazing”) of the polishing surface. Additionally, debris from the CMP process can clog the micro-channels through which slurry flows across the polishing surface. When this occurs, the polishing rate of the CMP process decreases; and this can result in non-uniform polishing between wafers or within a wafer. Periodic or continuous “in situ” conditioning creates a new texture on the polishing surface useful for maintaining the desired polishing rate and uniformity in the CMP process.
Conventional polishing pad conditioning is achieved by abrading the polishing surface mechanically with a conditioning disk. The conditioning disk has a rough conditioning surface typically comprised of embedded diamond points. The conditioning disk is brought into contact with the polishing surface either during a break in the CMP process, or while the CMP process is underway. Typically the conditioning disk is rotated in a position that is fixed with respect to the axis of rotation of the polishing pad, and sweeps out an annular conditioning region as the polishing pad is rotated. The conditioning process as described creates uniform conditioning in the conditioning region with the micro-channels typically having a circumferentially biased orientation because the linear velocity of the polishing table exceeds that of any point on the conditioning disk.
Non-uniform conditioning has been disclosed in the prior art to increase the flow of polishing medium on the polishing surface. For example, in U.S. Pat. No. 5,216,843, Breivogel et al. disclose a polishing pad having circumferential macro-grooves and radial microgrooves created by a diamond point conditioning process. The polishing pad of Breivogel et al., however, contains circumferential grooves that suffer from the undesirable effects of groove pattern transfer. This groove pattern transfer can produce non-uniform wafers having undesirable coherent structures that amount to under-polished wafer regions. Being typically tens of nanometers or greater in height, the coherent structures resulting from groove pattern transfer will be unacceptable for the future manufacture of semiconductor wafers.
There is a need for a polishing pad that will control distribution and flow of polishing medium in the CMP process and produce uniform wafers with a greater degree of planarity.